Question

8.) 2.) A bomb calorimeter, or a constant volume calorimeter, is a device often used to determine the heat of combustion of fuels and the energy content of foods.

In an experiment, a 1.0860 g sample of glutaric acid (C₅H₈O₄) is burned completely in a bomb calorimeter. The calorimeter is surrounded by 1.143×10³ g of water. During the combustion the temperature increases from 21.61 to 24.66 °C. The heat capacity of water is 4.184 J g^-1°C^-1.

The heat capacity of the calorimeter was determined in a previous experiment to be 761.1 J/°C.

Assuming that no energy is lost to the surroundings, calculate the molar heat of combustion of glutaric acid based on these data.

C₅H₈O₄(s) + 5O₂(g) = 4 H₂O(l) + 5 CO₂(g) + Energy

Answer 1

there is no heat loss so we can say that all heat released in combustion is absorbed by water and calorimeter.

heat absorbed by calorimeter = heat capacity of calorimeter $\times$ change in temperature of calorimeter

= 761.1 ( J/ ^oC) $\times$ (24.66 - 21.61)

= 2321.355 J

heat absorbed by water = mass of water $\times$ heat capacity of water $\times$ change in temperature of water

= 1.143 $\times$ 10³(g) $\times$ 4.184 ( J K^{-1 o}C^-1) $\times$ ( 24.66 - 21.61)

= 14586.05 J

we know that heat released in the combustion = heat absorbed by water + heat absorbed by calorimeter

= 14586.051 + 2321.355

  heat released in the combustion = 16907.406 J

this heat is released by combustion of 1.0860 g of glutaric acid.

convert this weight in mol, molar mass of glutaric acid is 132. so mol = 1.0860/132 = 8.2272 $\times$ 10^-3 mol

so heat released by combustion of 8.2272 $\times$ 10^-3 mol of glutaric acid. = 16907.406 J

then heat released by 1 mol of glutaric acid = 2055.043 KJ/mol

molar heat of combustion = 2055.043 KJ/mol